Conventionally, a plug main body 1 constructing the MPO type optical connector plug is provided with a ferrule 42 which is attached to a leading end of an optical fiber tape core wire FT, in a leading end (a front end) within a sleeve-like spring push 41 (which may also be referred to as a push sleeve), as shown in FIG. 21. Further, a spring 45 elastically energizing the ferrule 42 to a front side of the plug main body 1 is provided within the spring push 41. Further, the plug main body is provided with a tubular coupling 43 which is outward inserted to a concave part 49 of a housing 48 which is outward fitted to the spring push 41, is provided so as to be slidable in relation to the spring push 41 in a movable range which is secured in an axial direction thereof and is elastically energized to a front side of the plug main body 1 by the spring 46, and a boot 44 which is outward inserted to a rear end portion in an opposite side to a front end where the ferrule 42 of the spring push 41 is provided.
The insertion of the plug main body 1 into an adapter (not shown) is performed by pressing a portion which is positioned in a rear side from the coupling 43 in the plug main body 1, for example, the boot 44 toward the adapter (not shown) with a worker's finger. On the other hand, the detachment of the plug main body 1 from the adapter (not shown) is performed by pulling in the coupling 43 to the spring push 41 side against the elastic energizing force of the spring 46.
Here, a protection cap 200 is used for preventing the scratch from being attached to the leading end side of the ferrule 42 due to the dusts and the external force. More specifically, the protection cap 200 is formed by a cap main body 210 which is constructed by wide upper and lower side plate portions 210a and narrow right and left side plate portions 210b and is formed into an approximately flat rectangular tubular shape in an opening portion, as shown in FIGS. 18A, 18B, 18D, 19, 20A and 20B, and a leading end portion of the cap main body 210 forms an occluded portion 220 which is formed into an approximately flat conical shape so as to surround the ferrule 42. Further, a pair of key grooves 230 are formed in upper and lower symmetrical surfaces within the cap main body 210 for introducing and guiding a key projection (not shown) which is formed on an outer surface in a leading end (a front end) of the spring push 41.
The protection cap 200 is put on the leading end portion (the front end portion) of the spring push 41 and covers the leading end portion as shown in FIG. 21. In this case, the key projection of the spring push 41 is introduced and guided along the key groove 230 of the cam main body 210, and is locked by the leading end portion of the coupling 43.
Further, as shown in FIG. 18C, upper and lower pairs of ribs 240 which face laterally and are totally four ribs are formed in an inner wall surface of the wide side plate portion 210a in the cap main body 210, and the leading end portion of the spring push 41 is locked and retained by the ribs 240.
Further, patent document 1 conventionally discloses a dust cap in which an elastic locking piece is built therein. More specifically, in the dust cap, a pair of elastic latches positioned in an opposite side of the center axis include a cantilever arm portion which extends to a cantilever end portion from a base table of a sleeve (a cap main body), the arm portion extends to an open end from a closed end, and a groove portion is formed in a cavity of the sleeve (the cap main body) and forms a boundary portion of the cantilever arm portion.